Liquid crystal display (LCD) devices and other flat-panel display devices have recently been used as image display devices for television sets, personal computers in various kinds, car navigation devices and so on; in view of advantageous features of the flat-panel display devices, such as small depth dimension and small weight as well as small electric power consumption.
A light transmissive one of the LCD devices is for instance formed of; a liquid-crystal display panel in which liquid crystal layer is sandwiched by a pair of transparent substrates, and a surface-illuminant device disposed on backside, or non-displaying main face, of the liquid-crystal display panel as a light source for the display panel.
The surface-illuminant devices may be roughly classified into two categories; one is “direct backlight” in which a plurality of tube-shaped light sources such as fluorescent lamps arranged side by side at backside of the display panel; and the other is “edge-lit backlight” in which one or more tube-shaped light source is disposed to be in proximity along one or more edge of the light-guide plate as to emit light from a front-side main face of the light-guide plate.
In order to achieve smaller depth dimension and smaller weight of the LCD devices, depth dimension of the surface-illuminant devices have to be smaller. Thus, the “edge-lit backlights” have been prevalently used. The edge-lit backlight is for instance formed as follows. The light-guide plate is formed of a thin plate of acrylic resin or the like whose back face is printed with a light scattering pattern of milk-white appearance; and thereby, light-source light enters through an edge face of the light-guide plate and propagated through the plate, as to be emitted from front main face of the light-guide plate while being scattered by the light-scattering pattern on the back face of the plate.
The tube-shaped light source itself emits the light-source light through all around of the light-emitting surface, thus, a reflective element or a lamp reflector is arranged as to lead the light toward the edge face of the plate. The reflective element is usually formed of a film having a metal layer on a surface or a metal plate or formed of other electroconductive materials. The tube-shaped light source is generally formed of a fluorescent lamp such as a cold cathode fluorescent lamp. Thus, light-emitting efficiency declines when temperature of the lamp rises excessively; in an occasion of achieving high-brightness displaying as to increase heat generation. Moreover, local temperature rise in the liquid-crystal display plate may cause display unevenness. In view of the above, JP-A-2002-091330 (Japan Patent Application Publication No. 2002-091330) proposes disposing of a metal heatsink plate along back face of the light-guide plate as to dissipate the heat of the lamp reflector.
Nevertheless, such disposing of the metal heat-sink plate along back face may lead enhancement of level of electromagnetic noise because; the electromagnetic noise is transmitted from driver circuit board disposed along a back face of the metal heatsink plate to the heatsink plate and is propagated through the heat-sink plate. In view of the above, it is aimed to avert trouble of electromagnetic noise while achieving easy and reliable dissipation of heat from the light source.